How to unlock
They can be unlocked immediately for $1.99 for each individual special plague. The first special plague is unlocked by by beating all previous plagues in Brutal difficulty and beating one special plague on brutal unlocks the next. For some, these plagues can be more difficult than the standard and vise versa. They are unique, having different transmissions, symptoms, and abilities.
Each special plague also have their own theme and interface, each being unique when compared to any other plague. In Plague Inc., special plagues are located under a tab in the lower right-hand corner that says "Special," whilst in Plague Inc: Evolved, they are mixed with the original standard plagues (Although the sequence is not changed), and, due to plague types being put together, all can be unlocked by beating the previous one on normal. As with normal plagues, there are exclusive achievements they are associated with.
These are not a type of plague, but rather some built-in tweaks to make games easier. On Plague Inc., you must beat all the standard plague types on brutal to unlock the first four whist beating all standard plagues on mega brutal will unlock the rest.
On Plague Inc: Evolved, you must beat all plagues on normal for first four cheats, and all on brutal for the rest. Cheating will NOT register the player's score. Also, when cheating, the results show that the player had a negative score. Despite this, there are a few achievements related to winning games by using a specific cheat.